Spectral linearity and acquisition-chain effects in a LaBr₃:Ce scintillation detector

The response of a LaBr₃:Ce scintillation detector was investigated using digital and analog data acquisition systems operated under different photomultiplier tube (PMT) voltages. Energy calibration, energy resolution, coincidence timing performance, and Geant4-based simulations were used to evaluate the detector response. The detector exhibited better energy resolution than a NaI:Tl detector measured under comparable experimental conditions, while a coincidence timing resolution of 207 ps was obtained for the LaBr₃:Ce-BC408 detector system. The spectral non-linearity assessment was based on voltage dependent shifts of the fitted 511, 1275, and 1470 keV peak centroids. Although improved energy resolution values were observed at higher PMT operating voltages, the fitted peak positions exhibited increasing deviations from their nominal energies. Similar trends were observed in both digital and analog acquisition systems, indicating voltage dependent nonlinear effects within the complete detector readout chain. The comparison with the idealized Geant4 response was consistent with an acquisition chain related contribution, although it did not identify the specific component responsible. The study was limited to a restricted set of PMT operating voltages, and since the PMT gain and anode current were not independently characterized, the precise physical origin of the observed nonlinearity could not be uniquely determined.